1. Technical Field
The present invention relates to a method for fabricating a quadrupole mass filter (QMF) or a quadrupole ion trap (QIT).
2. Description of Related Art
Mass spectrometers generally rely on introducing a sample into a vacuum chamber where it is ionized by an ion source. The ions are separated according to their charge to mass ratio before they reach a detector. In a conventional quadrupole mass spectrometer (QMS), four circular electrodes disposed at each point of a compass create an electric field in their enclosed space. These electrodes are typically made from stainless steel up to I em in diameter and 15 cm long and require precision manufacturing. In WO-A-96/31901, there are disclosed electrodes in the form of metal coated glass fibres.
Recent developments in mass spectrometers have advanced rapidly with the main focus on building fully integrated devices that can be made portable whilst maintaining good performance. To achieve this, the miniaturization of mass spectrometer components such as mass analyzers has been pursued. Miniaturization of mass spectrometers is presently carried out by microelectromechanical systems (MEMS) based mainly on semiconductor microengineering with metal deposits. Since complex electrode geometries such as hyperbolic cannot be machined at micro-scale using MEMS, simpler geometries such as cylindrical and planar are used to give an approximation to a hyperbolic field.
One of the first miniature analyzers constructed using MEMS was a quadrupole mass filter (QMF) with cylindrical electrodes [Taylor S et al. Silicon based Quadrupole Mass Spectrometry using Microelectromechanical Systems. J. Vac. Sci. Technol. B 2001, 19, 557-562]. Other miniature mass analyzers include a time-of-flight mass filter [Wapelhorst E et al: Complex MEMS: a Fully Integrated TOF Micro Mass Spectrometer. Sensors and Actuators A 2007, 138, 22-27], a cylindrical micro ion trap that easily forms arrays [Blain M G et al: Towards the Hand-Held Mass Spectrometer: Design Considerations, Simulation and Fabrication of Micrometer-Scaled Cylindrical Ion Traps. Int. J. Mass Spectrom. 2004, 236, 91-104; Pau S et al: M. Microfabricated Quadrupole Ion Trap for Mass Spectrometer Applications. Phys. Rev. Lett. 2006, 96, 120801; and Van Amerom F H W et al: Microfabrication of Cylindrical Ion Trap Mass Spectrometer Arrays for Handheld Chemical Analyzers. Chem Eng. Comm. 2008, 195, 98-114], a rectilinear ion trap with planar electrodes [Song Y et al: Novel Linear Ion Trap Mass Analyzer Composed of Four Planar Electrodes. J. Am. Soc. Mass Spectrom. 2006, 17, 631-639] and a halo ion trap [Austin D E et al: Halo Ion Trap Mass Spectrometer. Anal. Chem. 2007, 79, 2927-2932]. Ion source miniaturization has also advanced with the realization of a carbon nanotube electron impact ion source [Bower C A et al: On-Chip Electron Impact Ion Source using Carbon Nanotube Field Emitters. Appl. Phys. Lett. 2007, 90, 124102].
U.S. Pat. No. 5,852,270 discloses a wire-cut method for manufacturing a miniature quadrupole.